Pro's for a Mechanical APV:
Ability to sub-ohm. Early regulated devices were not designed to sub-ohm; recently the higher wattage regulated APV's can vape sub-ohm, but with all of that power the same effect can be obtained with normal resistance coils.
Durability and longevity. With no internal electronics to fail, a mech is considered to be a more durable choice over a regulated APV.
Aesthetics. Many prefer the simple and elegant appearance of a mechanical.
Simplicity. A mechanical is simply a glorified battery holder, fire button, and 510 connector.
Cons for a mechanical APV:
No processor protection circuitry. This feature protects against many short circuits, reverse battery protection, over-heating, over-discharging the battery, etc. Without this feature, YOU THE USER must be constantly aware of potential dangers of short circuits.
The quality of the vaping experience will gradually and progressively decline over the course of the battery used between charges.
The only way to change the vaping experience is to change the atomizer (coil) resistance.
Pro's for Regulated APV's:
Protection circuitry against short circuits.
Power regulation. You can increase or decrease the voltage or wattage to suit your vaping preference. It will also keep your chosen power output constant regardless of the charge on the battery.
Built-in voltage and resistance meters.
Some regulated mods use a built-in, rechargeable (non-removeable) battery using a common USB charging cable.
Cons of regulated APV:
Often not as durable as a mechanical mod, because of the internal electrical components.
Until the advent of the more recent high wattage APV's, they could not power sub-ohm.
Aesthetics. Often not as physically attractive as many of the finer mechanical mods.
_____________________
I use both a regulated tube mod and a mechanical tube mod, on a daily basis. I like both, for different reasons. I'm not particularly a fan of the box mods.